Have you considered making all peripheral i2c based so you could just run them off of a single plug that you could make an adapter for? I haven’t played with it yet but I’m pretty sure Ramps has i2c pins on it.
Sorry for such a long delay in a response, work had me locked down for a while. From my experience with I2C, it works best when you have small distance involved. The technology was designed for chip to chip communication, which is generally mm or cm. To get to the UTM from the Pi would be order of magnitudes further (~3m). Put simply, you’d be inviting all sorts of issues.
That being said, if you were going to home spin such a critter, some people have done just what you’re looking for with a Pi, albeit not on the Farmbot.
“The vast majority of applications use I²C in the way it was originally designed – peripheral ICs directly wired to a processor on the same printed circuit board, and therefore over relatively short distances of less than a foot, without a connector. However a few applications use I²C to communicate between two boards, in some cases over a dozen meters apart, using pairs of I²C bus buffers to boost the signal or re-encode it as a differential signal traveling over CAT5 or other cable.” – Wiki link
These buffers and signal encoders would require power, so you’d have to spin your own board and then provide power. At that point though, you might as well put a small processor / microcontroller on the UTM, slap on a CAT5/6 jack and just use Ethernet.
Wow. Very informative response. I appreciate it.